簡介
本文用C#實現了一個最簡單的HTTP服務器類，你可以將它嵌入到自己的項目中，或者也可以閱讀代碼來學習關於HTTP協議的知識。
背景
高性能的WEB應用一般都架設在強大的WEB服務器上，例如IIS, Apache, 和Tomcat。然而，HTML是非常靈活的UI標記語言，也就是說任何應用和后端服務都可以提供HTML的生成支持。在這個小小的例子中，像IIS,、Apache這樣的服務器消耗的資源太大了，我們需要自己實現一個簡單的HTTP服務器，將它嵌入到我們的應用中用來處理WEB請求。我們僅需要一個類就可以實現了，很簡單。
代碼實現
首先我們來回顧一下如何使用類，然后我們再來分析實現的具體細節。這里我們創建了一個繼承於HttpServer的類，並實現了handleGETRequest 和handlePOSTRequest 這兩個抽象方法：
public class MyHttpServer : HttpServer { public MyHttpServer(intport):base(port) { } public override void handleGETRequest(HttpProcessor p) { Console.WriteLine("request: {0}", p.http_url); p.writeSuccess(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("Current Time: " + DateTime.Now.ToString()); p.outputStream.WriteLine("url : {0}", p.http_url); p.outputStream.WriteLine("<form method=post action=/form>"); p.outputStream.WriteLine("<input type=text name=foo value=foovalue>"); p.outputStream.WriteLine("<input type=submit name=bar value=barvalue>"); p.outputStream.WriteLine("</form>"); } public override void handlePOSTRequest(HttpProcessor p, StreamReader inputData) { Console.WriteLine("POST request: {0}", p.http_url); stringdata = inputData.ReadToEnd(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("<a href=/test>return</a><p>"); p.outputStream.WriteLine("postbody: <pre>{0}</pre>", data); } }
當開始處理一個簡單的請求時，我們就需要單獨啟動一個線程來監聽一個端口，比如8080端口：
HttpServer httpServer = new MyHttpServer(8080); Thread thread = new Thread(newThreadStart(httpServer.listen)); thread.Start();
如果你編譯運行這個項目，你會在瀏覽器http://localhost:8080地址下看到頁面上生成的示例內容。讓我們來簡單看一下這個HTTP服務器引擎是怎么實現的。
這個WEB服務器由兩個組件構成，一個是負責啟動TcpListener來監聽指定端口的HttpServer類，並且用AcceptTcpClient()方法循環處理TCP連接請求，這是處理TCP連接的第一步。然后請求到達“已指定“的端口，接着就會創建一對新的端口，用來初始化客戶端到服務器端的TCP連接。這對端口便是TcpClient的session，這樣就可以保持我們的主端口可以繼續接收新的連接請求。從下面的代碼中我們可以看到，每一次監聽程序都會創建一個新的TcpClien，HttpServer類又會創建一個新的HttpProcessor，然后啟動一個線程來操作。HttpServer類中還包含兩個抽象方法，你必須實現這兩個方法。
public abstract class HttpServer { protected int port; TcpListener listener; boolis_active = true; publicHttpServer(intport) { this.port = port; } public void listen() { listener = newTcpListener(port); listener.Start(); while(is_active) { TcpClient s = listener.AcceptTcpClient(); HttpProcessor processor = newHttpProcessor(s, this); Thread thread = newThread(newThreadStart(processor.process)); thread.Start(); Thread.Sleep(1); } } public abstract void handleGETRequest(HttpProcessor p); public abstract void handlePOSTRequest(HttpProcessor p, StreamReader inputData); }
這樣，一個新的tcp連接就在自己的線程中被HttpProcessor處理了，HttpProcessor的工作就是正確解析HTTP頭，並且控制正確實現的抽象方法。下面我們來看看HTTP頭的處理過程，HTTP請求的第一行代碼如下：
GET /myurl HTTP/1.0
在設置完process()的輸入和輸出后，HttpProcessor就會調用parseRequest()方法。
public void parseRequest() { String request = inputStream.ReadLine(); string[] tokens = request.Split(' '); if(tokens.Length != 3) { throw new Exception("invalid http request line"); } http_method = tokens[0].ToUpper(); http_url = tokens[1]; http_protocol_versionstring = tokens[2]; Console.WriteLine("starting: " + request); }
HTTP請求由3部分組成，所以我們只需要用string.Split()方法將它們分割成3部分即可，接下來就是接收和解析來自客戶端的HTTP頭信息，頭信息中的每一行數據是以Key-Value（鍵-值）形式保存，空行表示HTTP頭信息結束標志，我們代碼中用readHeaders方法來讀取HTTP頭信息：
public void readHeaders() { Console.WriteLine("readHeaders()"); String line; while((line = inputStream.ReadLine()) != null) { if(line.Equals("")) { Console.WriteLine("got headers"); return; } intseparator = line.IndexOf(':'); if(separator == -1) { throw new Exception("invalid http header line: " + line); } String name = line.Substring(0, separator); intpos = separator + 1; while((pos < line.Length) && (line[pos] == ' ')) { pos++;// 過濾掉所有空格 } string value = line.Substring(pos, line.Length - pos); Console.WriteLine("header: {0}:{1}",name,value); httpHeaders[name] = value; } }
到這里，我們已經了解了如何處理簡單的GET和POST請求，它們分別被分配給正確的handler處理程序。在本例中，發送數據的時候有一個棘手的問題需要處理，那就是請求頭信息中包含發送數據的長度信息content-length，當我們希望子類HttpServer中的handlePOSTRequest方法能夠正確處理數據時，我們需要將數據長度content-length信息一起放入數據流中，否則發送端會因為等待永遠不可能到達的數據和阻塞等待。我們用了一種看起來不那么優雅但非常有效的方法來處理這種情況，即將數據發送給POST處理方法前先把數據讀入到MemoryStream中。這種做法不太理想，原因如下：如果發送的數據很大，甚至是上傳一個文件，那么我們將這些數據緩存在內存就不那么合適甚至是不可能的。理想的方法是限制post的長度，比如我們可以將數據長度限制為10MB。
這個簡易版HTTP服務器另一個簡化的地方就是content-type的返回值，在HTTP協議中，服務器總是會將數據的MIME-Type發送給客戶端，告訴客戶端自己需要接收什么類型的數據。在writeSuccess()方法中，我們看到，服務器總是發送text/html類型，如果你需要加入其他的類型，你可以擴展這個方法。
完整代碼：
using System; using System.Collections; using System.IO; using System.Net; using System.Net.Sockets; using System.Threading; namespace Bend.Util { public class HttpProcessor { public TcpClient socket; public HttpServer srv; private Stream inputStream; public StreamWriter outputStream; public String http_method; public String http_url; public String http_protocol_versionstring; public Hashtable httpHeaders = new Hashtable(); private static int MAX_POST_SIZE = 10 * 1024 * 1024; // 10MB public HttpProcessor(TcpClient s, HttpServer srv) { this.socket = s; this.srv = srv; } private string streamReadLine(Stream inputStream) { int next_char; string data = ""; while (true) { next_char = inputStream.ReadByte(); if (next_char == '\n') { break; } if (next_char == '\r') { continue; } if (next_char == -1) { Thread.Sleep(1); continue; }; data += Convert.ToChar(next_char); } return data; } public void process() { // we can't use a StreamReader for input, because it buffers up extra data on us inside it's // "processed" view of the world, and we want the data raw after the headers inputStream = new BufferedStream(socket.GetStream()); // we probably shouldn't be using a streamwriter for all output from handlers either outputStream = new StreamWriter(new BufferedStream(socket.GetStream())); try { parseRequest(); readHeaders(); if (http_method.Equals("GET")) { handleGETRequest(); } else if (http_method.Equals("POST")) { handlePOSTRequest(); } } catch (Exception e) { Console.WriteLine("Exception: " + e.ToString()); writeFailure(); } outputStream.Flush(); // bs.Flush(); // flush any remaining output inputStream = null; outputStream = null; // bs = null; socket.Close(); } public void parseRequest() { String request = streamReadLine(inputStream); string[] tokens = request.Split(' '); if (tokens.Length != 3) { throw new Exception("invalid http request line"); } http_method = tokens[0].ToUpper(); http_url = tokens[1]; http_protocol_versionstring = tokens[2]; Console.WriteLine("starting: " + request); } public void readHeaders() { Console.WriteLine("readHeaders()"); String line; while ((line = streamReadLine(inputStream)) != null) { if (line.Equals("")) { Console.WriteLine("got headers"); return; } int separator = line.IndexOf(':'); if (separator == -1) { throw new Exception("invalid http header line: " + line); } String name = line.Substring(0, separator); int pos = separator + 1; while ((pos < line.Length) && (line[pos] == ' ')) { pos++; // strip any spaces } string value = line.Substring(pos, line.Length - pos); Console.WriteLine("header: {0}:{1}",name,value); httpHeaders[name] = value; } } public void handleGETRequest() { srv.handleGETRequest(this); } private const int BUF_SIZE = 4096; public void handlePOSTRequest() { // this post data processing just reads everything into a memory stream. // this is fine for smallish things, but for large stuff we should really // hand an input stream to the request processor. However, the input stream // we hand him needs to let him see the "end of the stream" at this content // length, because otherwise he won't know when he's seen it all! Console.WriteLine("get post data start"); int content_len = 0; MemoryStream ms = new MemoryStream(); if (this.httpHeaders.ContainsKey("Content-Length")) { content_len = Convert.ToInt32(this.httpHeaders["Content-Length"]); if (content_len > MAX_POST_SIZE) { throw new Exception( String.Format("POST Content-Length({0}) too big for this simple server", content_len)); } byte[] buf = new byte[BUF_SIZE]; int to_read = content_len; while (to_read > 0) { Console.WriteLine("starting Read, to_read={0}",to_read); int numread = this.inputStream.Read(buf, 0, Math.Min(BUF_SIZE, to_read)); Console.WriteLine("read finished, numread={0}", numread); if (numread == 0) { if (to_read == 0) { break; } else { throw new Exception("client disconnected during post"); } } to_read -= numread; ms.Write(buf, 0, numread); } ms.Seek(0, SeekOrigin.Begin); } Console.WriteLine("get post data end"); srv.handlePOSTRequest(this, new StreamReader(ms)); } public void writeSuccess() { outputStream.WriteLine("HTTP/1.0 200 OK"); outputStream.WriteLine("Content-Type: text/html;charset=utf-8"); outputStream.WriteLine("Connection: close"); outputStream.WriteLine(""); } public void writeFailure() { outputStream.WriteLine("HTTP/1.0 404 File not found"); outputStream.WriteLine("Connection: close"); outputStream.WriteLine(""); } } public abstract class HttpServer { protected int port; TcpListener listener; bool is_active = true; public HttpServer(int port) { this.port = port; } public void listen() { listener = new TcpListener(port); listener.Start(); while (is_active) { TcpClient s = listener.AcceptTcpClient(); HttpProcessor processor = new HttpProcessor(s, this); Thread thread = new Thread(new ThreadStart(processor.process)); thread.Start(); Thread.Sleep(1); } } public abstract void handleGETRequest(HttpProcessor p); public abstract void handlePOSTRequest(HttpProcessor p, StreamReader inputData); } public class MyHttpServer : HttpServer { public MyHttpServer(int port) : base(port) { } public override void handleGETRequest(HttpProcessor p) { Console.WriteLine("request: {0}", p.http_url); p.writeSuccess(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("Current Time: " + DateTime.Now.ToString()); p.outputStream.WriteLine("url : {0}", p.http_url); p.outputStream.WriteLine("<form method=post action=/form>"); p.outputStream.WriteLine("<input type=text name=foo value=foovalue>"); p.outputStream.WriteLine("<input type=submit name=bar value=barvalue>"); p.outputStream.WriteLine("</form>"); } public override void handlePOSTRequest(HttpProcessor p, StreamReader inputData) { Console.WriteLine("POST request: {0}", p.http_url); string data = inputData.ReadToEnd(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("<a href=/test>return</a><p>"); p.outputStream.WriteLine("postbody: <pre>{0}</pre>", data); } } public class TestMain { public static int Main(String[] args) { HttpServer httpServer; if (args.GetLength(0) > 0) { httpServer = new MyHttpServer(Convert.ToInt16(args[0])); } else { httpServer = new MyHttpServer(8080); } Thread thread = new Thread(new ThreadStart(httpServer.listen)); thread.Start(); return 0; } } }